Terrys right, i did both however as the sump plug in the trans is magnetic and has a fair amount of sludge on it. I reused the old gasket and it hasn't leaked. Did the remove sump plug and gasket, dump the fluid (about 3l came out) The refit the plug after cleaning it all up, then removed the oil cooler return line block of other end of line and run the engine in all gears with the brake on. it pumps the oil out til air bubbles are shown. About another half a litre. Then re-fill 2l into the dipstick ipe run the trans again and repeat th drain through the cooler line til air comes out...do this twice or until fluid flushing is coming out bright red. Then replace and tighten everything and rifill... careful on the levels, drive gently in all gears then re-check the levels. I noticed a more eager shift and a more responisve shift to the prevailing conditions after the flush, although not necessarily smoother. PS there is a good HOW TO guide on with pics etc. All the best.